The email also appeared to take a dig at his fellow billionaire rivals Michael Bloomberg and Tom Steyer as “people who can spend millions of their own dollars on a campaign,” though Buttigieg did not name them.
“Some of our competitors, like Bernie Sanders, have even run for president before — and that means that they had a head start on things like building their fundraising lists,” the email reads. “Having several million people on your email list allows you to do things like raise $4 million in two days — something Bernie says he did in the 48 hours after the last debate.”
“If we are going to turn the page on our politics, we have to be able to compete with the people who have been working in Washington for years, and the people who can spend millions of their own dollars on a campaign. That means we need your help right now with another donation to this campaign,” it continues.
Buttigieg has previously aimed his fire on Sanders’s progressive counterpart, Sen. Elizabeth Warren (D-Mass.), clashing with her in the two previous primary debates.
The 37-year-old former mayor has run as an outsider to Washington, D.C., and has advocated a more moderate platform than Sanders or Warren.
Although Sanders was first elected to Congress in 1990, he has often been viewed as a Washington outsider for the majority of his career, supporting a number of progressive issues like “Medicare for All.”
Sanders most recently went against the mold on Thursday, when he joined nine other senators in voting against the U.S.-Mexico-Canada Agreement.
The Vermont senator has also pushed back against the Democratic Party establishment and took the political world by surprise in 2016 in his unexpectedly strong challenge to Democratic-establishment favorite, Hillary Clinton.
The Hill has reached out to the Sanders campaign for comment.